1. Field of the Invention
The present invention relates to a process for preparing organosilicon compounds containing organyloxy groups and also to their use in compositions which crosslink at room temperature.
2. Description of the Related Art
RTV1 sealants, that is, one-component sealants which are storable in absence of water and on ingress of water cure at room temperature to elastomers, are known. They are used in large quantities in the building industry as grouting and sealing materials. Curing is typically accompanied by formation, through hydrolysis, of acetic acid or alcohols.
Polymeric organosilicon compounds for RTV1 sealants that through hydrolysis liberate acetic acid can be prepared very easily. Simple mixing of long-chain organopolysiloxanes which contain silanol groups on the chain ends and organosilicon compounds which contain at least 2 bound acetoxy groups on silicon is sufficient. Within a few minutes the process referred to as end capping takes place. This means that the OH groups on the chain ends of the polymers react with the acetoxysilanes.
The preparation of polymeric organosilicon compounds for RTV1 sealants which liberate alcohol on hydrolysis is substantially more involved. Thus, for example, mixtures of organosilicon compounds with groups and alkoxysilanes do not react with one another, even at relatively high temperatures. If, however, catalysts such as tin compounds or titanium compounds are added, then the components react directly to three-dimensionally crosslinked products which are not useful in RTV1 compositions.
The reaction can often be controlled more effectively when employing alkoxysilanes, if the latter contain hydrolyzable groups which are more reactive than the alkoxy groups. Thus EP-B-98 369 describes the reaction of dihydroxydiorganopolysiloxanes with alkoxyoximosilanes, and U.S. Pat. No. 3,147,047 describes the reaction with alkoxyamidosilanes. The preparation of these hybrid silanes, however, is very involved. Moreover, it is usually very difficult to remove the resultant hydrolysis products from the reaction mixture.
Catalysts and catalyst systems which lead very quickly to the desired end capping reaction have been suggested, but these are so reactive that they lead to unwanted polymer rearrangements, such as, for example, the hydroxide ions described in EP-B-457 693, or require deactivation by disadvantageous precipitation from high-viscosity solutions, such as fluoride ions, which are disclosed in EP-B-678 541.
Less reactive catalysts generally require very long reaction times, and high temperatures as well. Thus U.S. Pat. No. 5,055,502 claims zinc complexes such as zinc diacetylacetonate, as catalysts. The end capping reactions take place over 1 hour at 80° C. with the reaction mixture being stirred. EP-B-304 701 B1 teaches the use of acidic amine salts as catalysts. The end capping reactions take place over 1 to 3 hours at 70 to 100° C. with the reaction mixture being stirred.
US published application 2005/0234208 describes the reaction of linear polydimethylsiloxanes containing hydroxyl end groups with what are called α-silanes, such as N-(cyclohexylaminomethyl)triethoxysilane, for example. The reaction, after the mixing of polydimethylsiloxanes having OH end groups with α-silanes, takes place over 15 to 60 minutes at room temperature with a planetary mixing system, and also with the addition of butyllithium as catalyst.